This artist's illustration shows 'Oumuamua racing toward the outskirts of our solar system, and is annotated with the locations of the planetary orbits. As the complex rotation of the object makes it difficult to determine the exact shape, there are many models of what it could look like. › Larger view

Using
observations from NASA's Hubble Space Telescope and ground-based observatories,
an international team of scientists has confirmed 'Oumuamua (oh-MOO-ah-MOO-ah), the first known interstellar object to travel
through our solar system, got an
unexpected boost in speed and shift in trajectory as it passed through the
inner solar system last year.

"Our high-precision
measurements of 'Oumuamua's position revealed that there was something
affecting its motion other than the gravitational forces of the Sun and planets," said Marco Micheli of ESA's (European
Space Agency) Space Situational Awareness Near-Earth Object Coordination Centre
in Frascati, Italy, and lead author a paper describing the team's findings.

This video explains how observatories, including NASA's Hubble Space Telescope, found that 'Oumuamua gained an extra boost of speed, likely from comet-like jets of gas.

Analyzing the trajectory of the
interstellar visitor, co-author Davide Farnocchia of the Center for Near Earth Object Studies
(CNEOS) at NASA's Jet Propulsion Laboratory,
Pasadena, California, found that the speed boost was consistent with the
behavior of a comet.

"This
additional subtle force on 'Oumuamua likely is caused by jets of gaseous material expelled from its surface," said Farnocchia. "This same kind
of outgassing affects the motion of many comets in our solar system."

This animation shows the path of `Oumuamua as it passed through the inner solar system, and its location on Jan. 2, 2018, when it was last observed by NASA's Hubble Space Telescope. By then, 'Oumuamua had been boosted by 25,000 miles (40,000 kilometers) compared to where it would have been if only gravitational forces were affecting its motion.

Comets normally
eject large amounts of dust and gas when warmed by the Sun. But according to team
scientist Olivier Hainaut of the European Southern Observatory, "There were
no visible signs of outgassing from 'Oumuamua, so these forces were not
expected."

The team
estimates that 'Oumuamua's outgassing may have produced a very small amount
of dust particles -- enough to give the object a little kick in speed, but not enough
to be detected.

Karen Meech, an
astronomer at the University of Hawaii's Institute of Astronomy and co-author
of the study, speculated that small dust grains, present on the surface of most
comets, eroded away during 'Oumuamua's long journey through
interstellar space.

"The more
we study 'Oumuamua, the more exciting it gets," Meech said. "I'm
amazed at how much we have learned from a short, intense observing
campaign. I can hardly wait for the next interstellar object!"

'Oumuamua, less than half a mile in length, now is farther
away from our Sun than Jupiter and traveling away from the Sun at about 70,000 mph
as it heads toward the outskirts of the solar system. In only another four
years, it will pass Neptune's orbit on its way back into interstellar space.

Because 'Oumuamua
is the first interstellar object ever observed in our solar system, researchers
caution that it's difficult to draw general conclusions about this newly-discovered
class of celestial bodies. However, observations point to the possibility that other
star systems regularly eject small comet-like objects, and there should be more
of them drifting among the stars. Future ground- and space-based surveys could
detect more of these interstellar vagabonds, providing a larger sample for
scientists to analyze.